The present invention generally relates to the use of polymerized crystalline colloidal array (PCCA) chemical sensing materials to detect concentrations of certain chemical species in high ionic strength solutions, such as bodily fluids or environmental testing. The PCCA materials are optical, hydrogel-based materials that act as sensors for certain chemical species because of the PCCAs"" diffraction properties. More specifically, the present invention relates to utilizing the PCCA chemical sensing materials to detect the presence of varying concentrations of a chemical species, such as lead, in bodily fluids.
The development of novel methodologies for sensing the concentration of certain chemical species in high ionic strength solutions (such as bodily fluids) is technologically challenging because of the complexity of such solutions and because the concentrations of key chemical species within the fluids may be relatively low. Additionally, the high ionic strength of such solutions often decrease the sensitivity of certain chemical sensing methodologies already known in the art, such as the methods disclosed in U.S. Pat. No. 6,187,599 of Asher et al., the specification of which is hereby incorporated by reference herein in its entirety.
In disclosures such as U.S. Pat. No. 6,187,599, it has been demonstrated that PCCA materials can be used to detect low concentrations of chemical species such as Pb2+ in low ionic strength solutions. Thus, a need exists for a method for measuring the presence of certain chemical species, even in high ionic strength environments.
The chemical sensing ability of the polymerized crystalline colloidal array materials disclosed in U.S. Pat. No. 6,187,599 results from changes in the volume of the hydrogel which embeds the crystalline colloidal array in response to a chemical species. These volume changes cause shifts in the wavelength of light diffracted by the PCCA, which results in a detectable color change.
The changes in volume of the hydrogel of the crystalline colloidal array result from changes in the free energy of the hydrogel. For example, immobilization of charge on the hydrogel due to the presence of a chemical species causes the hydrogel to undergo a volume phase transition. Specifically, when a polymerized crystalline colloidal array material is acting as a sensor for the presence of Pb2+, it may comprise a chemical stimulus-recognition component having a crown ether which binds to Pb2+. The binding of the Pb2+ results in immobilization of charge and the hydrogel subsequently undergoes a volume change. Similarly, when a PCCA material is acting as a sensor for the presence of other chemical species, such as glucose, the glucose oxidase enzyme may be attached to the hydrogel as the chemical stimulus recognition component, and charge is immobilized on the reduced flavin of the glucose oxidase-upon binding of the glucose, causing a change in volume of the hydrogel.
However, these previously disclosed methods for using PCCA materials as chemical sensors have demonstrated that high ionic strength solutions decrease the magnitude of the hydrogel volume change. Thus, these prior art methods are limited in detecting the presence of certain chemical species in bodily fluids which have high ionic strengths. Thus, as previously noted, a need exists for a method that would allow PCCA chemical sensing materials to function effectively as sensors of certain chemical species including, but not limited to, Pb2+, glucose, and cholesterol, even in high ionic strength environments.
With respect to utilizing PCCA chemical sensing materials to detect the presence of Pb2+, developing a method for detecting Pb2+ in high ionic strength solutions, such as bodily fluids, would address many medical and environmental problems, since Pb2+ is such a serious medical and environmental toxin. Lead (specifically Pb2+) can cause disease and death at concentrations as low as 700 parts per billion (ppb) in blood. Bodily concentrations of Pb2+ as low as 100 ppb or 500 nM have been correlated with decreased IQ levels in children. Thus, universal screening of children for Pb2+ in blood was enunciated as a public health goal by both the PHS and the Center for Disease Control in 1991.
Both the United States (Center for Disease Control) and international health organizations (World Health Organization) have set guidelines that recommend that lead in bodily fluids be measured with a detection limit of 10 xcexcg/dL or 480 nM, within a measuring range of (0-60) xcexcg/dL or (0-2.88) xcexcM lead, and with a precision of less than 2 xcexcg/dL or 10%, whichever is greater. Current estimates from the National Center for Health Statistics indicate that 3.2% of American children have blood Pb2+ levels above 480 nM, while 20% of minority children in poverty have blood Pb2+ levels above 480 nM.
Universal Pb2+ screening was abandoned by the federal government in 1997 because of economic reasons, despite the large numbers of children at risk. Even when performed in large numbers, the laboratory cost for analyzing a single blood specimen for Pb2+ is $8-15. The costs of drawing the blood, communicating the results, and more importantly, finding and retrieving the child, raise the price per case to $50 or more. Thus, a rapid, simple and inexpensive quantitative serum Pb2+ test that could identify a child with an elevated Pb2+ level while the child is still present in the office would reduce the costs dramatically and would have considerable impact on the prevention of serious lead poisoning and its neurobehavioral effects. Most importantly, universal screening may become a feasible goal.
Many different methods have been used to detect lead in biological matrices such as bodily fluids. Such techniques include: atomic absorption spectrometry, neutron activation analysis, spark source mass spectroscopy, X-ray fluorescence, proton-induced X-ray emission, inductively coupled plasma atomic emission spectroscopy, isotope dilution mass spectrometry, anodic stripping voltammetry (ASV), and differential pulse ASV.
Reeder et al. disclose an ASV detection method coupled with an electrochemical sensor by screen-printing techniques to detect lead in the 10xe2x88x926 to 10xe2x88x929 M concentration range. See Reeder et al., Sensors and Actuators B, Vol. 52, pp. 58-64 (1998). Also, an electrochemical analyzer coupled to screen-printed disposable sensors for the field screening of trace lead is disclosed by Yarnitzky et al. to detect lead levels of 20-300 xcexcg/L in drinking water (low ionic strength). See Yarnitzky et al., Talanta, Vol. 51, pp. 333-38 (2000).
Furthermore, Yu et al. disclose a lead sensor made by first derivatizing the Pb2+ with sodium tetraethylborate to form tetraethyllead, which is then extracted from the headspace over the sample by solid-phase microextraction gas chromatography. See Yu et al., Anal. Chem., Vol. 71, pp. 2998-3002 (1999). The limit of detection for the Yu et al. disclosure was 5-10 ppb for urine and blood samples.
Also, de la Riva et al. disclose a flow-injection system which utilizes room temperature phosphorescent quinolinesulphonic acid lead chelates immobilized on an anion exchange resin to detect lead in seawater and the ng/mL level. See de la Riva et al., Anal. Chim. Acta, Vol. 395, pp. 1-9 (1999). These methods are both costly and time consuming.
None of the above-described prior art, however, discloses an effective method to detect chemical species, such as Pb2+ in bodily fluids and other high ionic strength solutions which is time efficient and cost-effective as does the present method.
An object of the present invention is to provide a method for using sensor devices composed of polymerized crystalline colloidal array (PCCA) materials to detect the presence of certain chemical species in high ionic strength solutions. The process of chemical sensing by the polymerized crystalline colloidal arrays previously disclosed in U.S. Pat. No. 6,187,599 of Asher et al. results from changes in volume of the hydrogel in which the crystalline colloidal array is embedded. This volume change results from immobilization of charge on the hydrogel due to the presence of a chemical species, and causes shifts in the wavelength of light diffracted by the crystalline colloidal array, wherein such a wavelength change is sensed by the color change.
However, high ionic strength solutions decrease the magnitude of the hydrogel volume change, which results from charge immobilization by the sensor. Thus, the present invention is directed to a method for removing much of the interference caused by high ionic strength solutions.
An object of the present invention is to first equilibrate the sensor (composed of the polymerized crystalline colloidal array) in the solution containing the specific chemical species, and subsequently place the sensor into a low ionic strength solution, such as, but not limited to, water. As a result of this step of placing the sensor in the low ionic solution strength, the ionic compounds giving rise to the high ionic strength solution diffuse out of the hydrogel, while the bound chemical species are retarded in the PCCA material and a transient swelling of the hydrogel occurs. The magnitude of this transient swelling is proportional to the chemical species concentration.
Therefore, a further object of the present invention is to provide a method whereby a transient response of sensor materials (composed of a polymerized crystalline colloidal array) is used to detect the concentration of certain chemical species in high ionic strength solutions.
Still another object of the present invention is to provide an optrode for use in high ionic strength solutions, wherein the optrode comprises the polymerized crystalline colloidal array and an optical fiber assembly which illuminates the polymerized crystalline colloidal array, collects the back-diffracted light, and images it to a spectrometer for analysis.
One skilled in the art will appreciate that the various embodiments disclosed herein, as well as other embodiments within the scope of the invention, will have numerous applications in the environmental, medical and chemical fields.